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Understanding Snapshots on ESX4.1

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  • Understanding Snapshots on ESX4.1

    So I'm fairly new to the topic of snapshots and really just want to figure out whether I am understanding this properly.

    I've done my homework and have read up quite a bit on snapshots. The general recommendation seems to be: Don't run your VM off snapshots and if you do, don't do it for very long.

    Well, that is kind of where my problem starts. I know what I WANT to do but I don't know whether I'm doing it right.

    So, let's start with the what I WANT to do:

    I've got a test / dev environment with 2 Win 2008 servers and 2 XP workstations that play together. This environment was created specifically for testing / playing purposes so what I want to do is to give access to whoever needs access and then when they are done with it revert all 4 machines to the working state I've prepared.

    How I WANT to do it:

    I have prepared all four servers to a working state. Ideally I would now snapshot all of them and call the snapshot "working state" or whatever. Then, every single time the environment is "handed back to me" I would revert to "working state".

    This where the questions start.

    Obviously I am now in a position where I will be running off a snapshot full time ("working state"). If I understood correctly that would mean that a) performance is depreciated b) the snapshot will grow and grow.

    However, every single time I get the environment back, I will revert to said snapshot which in my mind is the same as dropping the incremental data meaning it shouldn't grow indefinitely.
    I've also load tested the workstations and servers running off snapshots and am happy with the performance.

    So, what is this? Something that will work? That won't break down the line because I've overlooked something? Blatantly a really bad idea?

    Any comments greatly appreciated.

    Thanks, Martin

  • #2
    Re: Understanding Snapshots on ESX4.1

    As you;ve mentioned it's not advisable to run snapshots for long periods of time. I inherited an environment where the pervious administrator used snapshots as s point in time backup .

    Are you using vCenter? If you are then you could always clone the server. Once it's handed back to you you could delete the VM and then clone the clone. You might have issues with it loosing it's domain membership depending how long it's been offline (The "in-use" VM could have changed the computer account password within AD) Worst case scenario is to remove, reset the computer account and add back to the domain.

    Hope this helps.

    Michael Armstrong
    MCITP: EA, MCTS, MCSE 2003, MCSA 2003: Messaging, CCA, VCP 3.5, 4, 5, VCAP5-DCD, VCAP5-DCA, ITIL, MCP, PGP Certified Technician

    ** Remember to give credit where credit is due and leave reputation points sigpic where appropriate **


    • #3
      Re: Understanding Snapshots on ESX4.1

      The snapshot will never grow larger than the actual size of the virtual disk.
      So if you have a VMDK that is defined as 40GB, each snapshot file cannot grow to larger than 40GB.

      Have you thought about using non-persistent disks? they only keep until the next reboot - but it might suit your needs

      If the performance is acceptable - you will not need to consolidate the sanpshots, then you could be ok
      Technodrone|@maishsk|Author of VMware vSphere Design
      VMware vExpert 2013-2010,VCAP5-DCA/DCD,VCP
      MSCA 2000/2003, MCSE 2000/2003
      A proud husband and father of 3 girls
      If you find the information useful please don't forget to give reputation points sigpic.

      Have a good one!!


      • #4
        Re: Understanding Snapshots on ESX4.1

        Thank you very much for the very helpful posts. I do apologize for not reporting back earlier but things are busy with Christmas lurking around the corner.

        Non-persistent disks - FANTASTIC. They're pretty much what I want. People can keep their changes until they shut down and hey presto it is back to how I want it to be. This makes really nice test beds. Thanks for pointing this out. What the link quotes is true I guess: There are some features of VMware deployments using VMs that donít get the press they deserve.

        I have now got a working solution (at least it is working for me) that, as mentioned previously, relies on running off snapshot. When people are done I just revert to snapshot (drop the delta) and they can start over again. As I'm not running off snapshot for a long period of time (or at least I always come back to the same snapshot) I have not seen substantial growth or decrease in performance yet, which is obviously good.

        The reason this is working quite well for me is that these are 3 servers and 2 workstations that play together and they all have to be reset at the same time so they don't go out of sync.
        I've written a little "one button reset" that interacts with VMWare Power CLI. Users just launch that tool, press one button, and it'll issue a soft shutdown to these five servers, then check whether they are off (and do a hard shutdown if necessary) and will then reset all five to snapshot and power them on again. Takes about 3 minutes.

        Happy users because they can test whatever they like. Happy admin because I don't have to run around resetting the environment - users can just do that themselves now

        Happy Christmas and again thanks for the responses, much appreciated!